A prospective, multicenter, clinical outcome study of the NANOS neck preserving stem in patients with degenerative hip joint disease.

Short-stemmed femoral shaft prostheses, have been introduced especially for
younger patients. These endo-prostheses are anchored exclusively in the
metaphysic and the proximal part of the diaphysis. Therefore, they are much
shorter than the classic standard stems. Short femoral neck implants are
claiming less interference with the biomechanics.

The NANOS femoral neck prosthesis has been developed based on clinical
experience of various *short stem prostheses* and is the third generation of
this type of prostheses. The implant requires only minimal bone resection.
Therefore a maximum amount of bone is preserved. The cancellous bone around the
metaphysic and the greater trochanter are retained to ensure load distribution
and transfer.
The surface roughness of the titanium plasma coating on one hand increases the
surface area and on the other hand ensures superior primary stability. The
additional calcium phosphate coating allows accelerating the osseointegration
process.

To prove that the NANOS prosthesis is a good prosthesis to be used in total hip
replacement surgery, with low revision rate (< 10%) after 10 years. This
percentage is known in the Swedish registry.
Second objective is to prove that clinical outcome (Harris Hip Score, HOOS,
UCLA and radiological findings) is comparable to clinical results of other
short stemmed femoral shaft prostheses, known from literature.

Prospective, multicenter, observational clinical outcome study.

This is an observational study with no extra interventions for the patients, as
just completing one questionnaire which can be done while waiting to see the
surgeon at control visits.